CN107529988B

CN107529988B - Atrial fibrillation detection

Info

Publication number: CN107529988B
Application number: CN201680018682.6A
Authority: CN
Inventors: 戴维·L·佩尔施巴谢; 迪帕·马哈詹; 霍华德·D·小西姆斯
Original assignee: Cardiac Pacemakers Inc
Current assignee: Cardiac Pacemakers Inc
Priority date: 2015-04-02
Filing date: 2016-03-28
Publication date: 2020-10-30
Anticipated expiration: 2036-03-28
Also published as: US20160287115A1; CN107529988A; ES2749127T3; US9999368B2; JP6525461B2; US10542902B2; EP3277372A1; JP2018511400A; WO2016160674A1; EP3277372B1; US20180242869A1

Abstract

An apparatus comprising: a sensing circuit configured to generate a sensed physiological signal representative of cardiac activity of a subject; and an arrhythmia detection circuit. The arrhythmia detection circuit is configured to: monitoring information corresponding to a ventricular depolarization (V-V) interval for use of the sensed physiological signal; determining a V-V interval distribution; determining a Heart Rate Density Index (HRDI) as a portion of a sample of the V-V interval distribution corresponding to the most frequently occurring V-V intervals in the distribution; and generate an indication of Atrial Fibrillation (AF) using the HRDI.

Description

Atrial fibrillation detection

Priority requirement

This application claims benefit of priority according to 35u.s.c. § 119(e) of U.S. provisional patent application serial No. 62/142,184, filed on 2/4/2015, which is incorporated herein by reference in its entirety.

Background

Ambulatory medical devices include Implantable Medical Devices (IMDs), wearable medical devices, handheld medical devices, and other medical devices. Some examples of IMDs include Cardiac Function Management (CFM) devices such as implantable pacemakers, Implantable Cardioverter Defibrillators (ICDs), subcutaneous implantable cardioverter defibrillators (S-ICDs), cardiac resynchronization therapy devices (CRTs), and devices that include combinations of these capabilities. These devices may be used to treat a patient or subject using electrical or other therapy, or to assist physicians or paramedics in patient diagnosis by internally monitoring the condition of the patient.

Some implantable medical devices may be diagnostic-only devices, such as Implantable Loop Recorders (ILRs) and subcutaneous implantable heart failure monitors (SubQ HFMs). The apparatus may include electrodes in communication with one or more sense amplifiers to monitor cardiac electrical activity within the patient, or may include one or more sensors to monitor one or more other internal patient parameters. The subcutaneous implantable device may include electrodes capable of sensing cardiac signals without direct contact with the patient's heart. Other examples of IMDs include implantable drug delivery systems or implantable devices with neurostimulation capabilities (e.g., vagus nerve stimulators, baroreflex stimulators, carotid sinus stimulators, spinal cord stimulators, deep brain stimulators, etc.).

Some examples of wearable medical devices include Wearable Cardioverter Defibrillators (WCDs) and wearable diagnostic devices (e.g., dynamic monitoring vests, holder monitors, cardiac event monitors, or mobile cardiac telemetry devices). The WCD may be a monitoring device that includes surface electrodes. The surface electrodes may be arranged to provide one or both of monitoring for providing a surface Electrocardiogram (ECG) and delivery of cardioverter and defibrillator shock therapy. In some examples, the wearable medical device may also include a monitoring patch worn by the patient, such as an adherable patch, or may be included on clothing worn by the patient.

Some examples of handheld medical devices include Personal Data Assistants (PDAs) and smart phones. The handheld device may be a diagnostic device that records an Electrocardiogram (ECG) or other physiological parameter while the device is resting in a patient's hand or held on the patient's chest.

CFM devices may be implantable, but in some cases may not include specialized atrial sensing capabilities. Additionally, some diagnostic-only implantable, wearable, and handheld devices do not include specialized atrial sensing capabilities. Patients with these types of devices may develop atrial arrhythmias, such as, for example, Atrial Fibrillation (AF). This is particularly true for heart failure patients who typically have a high incidence of AF. Knowledge that a particular patient is experiencing AF may be useful to physicians and clinicians for diagnostic purposes, or the performance of a medical device may be tailored to the patient's needs to provide the most effective patient treatment.

Disclosure of Invention

It may be desirable for the ambulatory medical device to correctly detect and identify arrhythmias. This may help to provide the most effective device-based therapy or non-device based therapy for the patient. The present subject matter relates to improving atrial fibrillation detection.

One example system of the present subject matter can include: a sensing circuit configured to generate a sensed physiological signal representative of cardiac activity of a subject; and one or more arrhythmia detection circuits. The arrhythmia detection circuit may be configured to: monitoring information corresponding to a ventricular depolarization (V-V) interval using the sensed physiological signal; generating a heart rate distribution using information corresponding to the V-V interval; determining a characteristic of a Heart Rate Density Index (HRDI); and uses the heart rate pattern and the characteristics of the HRDI to generate an indication of Atrial Fibrillation (AF).

This section is intended to provide a brief summary of the subject matter of the present patent application. And are not intended to provide an exclusive or exhaustive explanation of the invention. In addition to the statements made in this section, the detailed description is included to provide further information about the present patent application, such as a discussion of the dependent claims and the interrelationships of the dependent and independent claims.

Drawings

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The figures generally illustrate the various examples discussed in this document by way of example and not by way of limitation.

Fig. 1 is an illustration of an example of a portion of a medical device system including an IMD.

Fig. 2 and 3 are diagrams of further examples of IMDs.

Fig. 4 is an illustration of a portion of another example of a medical device system.

Fig. 5 shows a flow chart of an example of a method of operating an ambulatory medical device.

Fig. 6 shows a graph of an example of a heart rate distribution for a patient in a normal sinus rhythm.

Fig. 7 shows a graph of an example of a heart rate distribution of a patient in atrial fibrillation.

Fig. 8 shows heart rate pattern data and heart rate density index data for a population of patients in normal sinus rhythm.

Fig. 9 shows heart rate pattern data and heart rate density index data for a population of patients in atrial fibrillation.

Fig. 10 is a block diagram illustrating portions of an example of an ambulatory medical device.

Fig. 11 shows a representation of an example of a sensed physiological signal.

Fig. 12 shows a representation of another example of a sensed physiological signal including normal sinus rhythm and atrial fibrillation.

Fig. 13 is a flow chart of another example of a method of operating an ambulatory medical device.

Fig. 14 shows a block diagram of portions of another example of a medical device system.

Detailed Description

The ambulatory medical device can include one or more features, structures, methods, or combinations thereof described herein. For example, a cardiac monitor or cardiac stimulator may be implemented to include one or more of the advantageous features or processes described below. It is intended that such monitors, stimulators, or other mobile devices need not include all of the features described herein, but may be implemented to include selected features that provide unique structures or functions. Such devices may be implemented to provide various therapeutic or diagnostic functions.

Fig. 1 is an illustration of an example of a portion of a system 100 including an IMD 105. Examples of IMDs 105 include, but are not limited to, pacemakers, cardioverters, defibrillators, and other cardiac monitoring and therapy delivery devices that include cardiac devices that include or work in coordination with one or more neurostimulation devices, drugs, drug delivery systems, or other therapies. In one example, the illustrated system 100 is used to treat cardiac arrhythmias. The IMD 105 typically includes an electronics unit coupled to the heart of a patient or subject via one or more cardiac leads 115. The electronics unit of the IMD 105 typically includes components enclosed in a hermetically sealed housing sometimes referred to as a cartridge or "can". The system 100 also typically includes an IMD programmer or other external system 190, the external system 190 communicating one or more wireless signals 185 with the IMD 105, such as through the use of Radio Frequency (RF) or through one or more other telemetry methods.

The illustrated example includes a Right Ventricular (RV) lead 115 having a proximal end and a distal end. The proximal end is coupled to a header connector 107. The distal end is configured for placement in the RV. The RV lead 115 can include one or more of a proximal defibrillation electrode 116, a distal defibrillation electrode 118 (e.g., RV coil), an RV tip electrode 120A, and an RV ring electrode 120B. Defibrillation electrode 116 is typically incorporated into a lead body, such as in a location suitable for supraventricular placement in the superior vena cava (e.g., SVC coil). In some examples, RV lead 115 includes a ring electrode 132 (e.g., an SVC ring) near proximal defibrillation electrode 116. Defibrillation electrode 118 is incorporated into the lead body near the distal end, such as for placement in the RV.

RV electrodes

120A and 120B may form a bipolar electrode pair and are typically incorporated into a lead body at the distal end of the lead.

Electrodes

116, 118, 120A, and 120B are each electrically coupled to IMD 105, such as by one or more conductors extending within the lead body. The proximal defibrillation electrode 116, the distal defibrillation electrode 118, or an electrode formed on the can of the IMD 105 allows cardioversion or defibrillation pulses to be delivered to the heart. RV tip electrode 120A, RV ring electrode 120B or an electrode formed on the can of IMD 105 allows sensing of RV electrogram signals representative of RV depolarization and delivery of RV pacing pulses. The IMD 105 includes sense amplifier circuitry to provide amplification or filtering of the sensed signals. Sensing and pacing allows the IMD 105 to adjust the timing of ventricular contractions.

Some IMDs such as that shown in fig. 1 may not include any electrodes for sensing electrical activity in the atrium. For example, the IMD 105 may be an ICD with single ventricular chamber sensing. An ICD may include electrodes attached to a single ventricular lead and use intrinsic cardiac signals sensed with the ventricular electrodes (e.g., by rate sensing and/or depolarization signal morphology analysis) for arrhythmia detection and identification.

The IMD may be a diagnostic-only device and not provide electrical therapy to the patient. Such devices may include RV tip electrode 120A, RV ring electrode 120B or a combination of electrodes formed on the can of IMD 105 that allow sensing of ventricular depolarizations. Note that the particular arrangement of leads and electrodes shown in the illustrated example of fig. 1 is intended to be non-limiting.

Fig. 2 is an illustration of another example of a portion of a system 200 that includes an S-ICD 205. S-ICD 205 is subcutaneously implantable and includes lead 215. Lead 215 is also implanted subcutaneously and the proximal end of lead 215 is coupled to header connector 207. Lead 215 may include

electrodes

220A and 220B to sense ventricular depolarization (e.g., using far field sensing), but in the illustrated example, the lead does not include any electrodes that directly contact the heart. Lead 215 includes defibrillation electrode 218, which may be a coil electrode. S-ICD 205 may provide one or more of cardioversion therapy and defibrillation high energy shock therapy to the heart using defibrillation electrode 218 and electrodes formed on the can of S-ICD 205. In some examples, S-ICD 205 may also provide pacing pulses for anti-tachycardia therapy or bradycardia therapy. Note that no direct atrial sensing is provided in the arrangement of electrodes.

Fig. 3 is an illustration of an example of a leadless IMD. In the example shown, the IMD is a leadless pacemaker 305. The leadless pacemaker 305 is shown positioned at the endocardium within the ventricular cavity, but the leadless pacemaker 305 may be positioned at other locations of the heart. The leadless pacemaker 305 example has a cylindrical or bullet-shaped housing and may include one or more electrodes disposed along the cylindrical housing to sense electrical signals of the heart and/or provide electrical stimulation for pacing the heart. One or more electrodes may be used for communication. The leadless pacemaker 305 may include a mechanism 330 to secure the pacemaker to the myocardium. Examples of fixation mechanisms may include one or more teeth, one or more barbed teeth, and one or more helical fixation mechanisms. The electrodes used for the device placement shown in the examples may not provide direct atrial sensing.

Other examples of IMDs include Implantable Loop Recorders (ILRs), diagnostic devices without leads in the heart, and neurostimulators (including but not limited to vagal nerve stimulators, baroreceptor stimulators, and spinal cord stimulators) or other IMDs. These types of devices may not include electrodes positioned in the atrium.

Fig. 4 is an illustration of portions of another example of a medical device system 400. The system 400 may include one or more ambulatory medical devices, such as a conventional implantable or subcutaneous implantable medical device 405, a wearable medical device 410, or a handheld medical device 403. One or more medical devices may include communication circuitry (e.g., telemetry circuitry) to communicate an indication of AF to communication system 407. The communication system 407 may include an external communication device 412 and a remote system 414, the remote system 414 communicating with the external communication device 412 via a network 418 (e.g., the internet, a proprietary computer network, or a cellular telephone network). The remote system 414 may include a server 416 located remotely from the external communication device 412 and the subject to perform patient management functions. The external communication device 412 may include a programmer to program therapy parameters of the device-based therapy provided by the implantable medical device. One or both of the external communication device 412 and the remote system 414 may include a display for presenting an indication of AF to a user, such as a clinician.

Fig. 5 is a flow chart of an example of a method 500 of operating an ambulatory medical device. Method 500 provides for detecting AF using ambulatory medical treatment even though the ambulatory medical device may not include electrodes and sensing circuitry for performing direct atrial sensing.

At 505, information corresponding to a ventricular depolarization interval (or V-V interval) of the subject is monitored. The interval may be monitored in beats per minute (bpm) or in time (e.g., milliseconds). One skilled in the art will understand, when reading this document, that the interval between heart depolarizations can be used to determine heart rate, and the terms heart rate and interval can be used interchangeably in the methods described. A depolarization interval may be sensed at the right ventricle or the left ventricle. This information may include sampled values of the V-V interval. The distribution of the V-V intervals is determined.

In some examples, shown at 510, the heart rate pattern is determined using the V-V interval. Heart rate pattern refers to the heart rate that occurs most often in the heart beat interval or distribution of heart rates. Fig. 6 shows a graph of an example of a heart rate distribution for a Normal Sinus Rhythm (NSR). Most of the samples of the distribution lie between about 50bpm and 90 bpm. The distribution pattern is about 60bpm because this is the heart rate that occurs most often in the distribution.

Returning to FIG. 5 at 515, the Heart Rate Density Index (HRDI) is determined using the V-V interval. In some examples, the HRDI may be a portion of a sample of the V-V interval distribution corresponding to the V-V interval that occurs most frequently in the distribution. In some examples, the HRDI may be part of a distribution with a heart rate pattern with V-V intervals. In some variations, the HRDI is expressed as a fraction (e.g., a percentage) of the interval. In the example of fig. 6, HRDI is 81% corresponding to a heart rate mode of 60 bpm.

At 520 of fig. 5, an indication of AF is generated using heart rate mode and HRDI. Fig. 7 shows a graph of an example of a heart rate distribution of a patient in AF. It can be seen that the heart rate in AF is not as regular as in NSR. In the example of fig. 7, the heart rate mode is 90bpm and the HRDI is about 23%. The values of heart rate mode and HRDI can only be measured using the V-V interval. In this way, AF may be detected without including dedicated atrial sensing in the ambulatory medical device.

Fig. 8 shows heart rate pattern data and HRDI data for a population of patients in NSR. As can be seen in fig. 8, the data is mainly contained in the unshaded region of the heart rate pattern above 25% HRDI and below 100 bpm. Fig. 9 shows heart rate mode data and HRDI data for a population of patients in AF. As can be seen in fig. 9, the data is mainly contained in the unshaded areas of the HRDI below 25% and the heart rate pattern above 100 bpm.

In some variations, the HRDI is determined using the shape of the heart rate distribution. For example, the HRDI may be a measure of one or more of skew, kurtosis, and variance of the heart rate distributions of fig. 6 and 7.

According to some examples, the HRDI may be compared to a specified HRDI threshold. AF is detected when the HRDI satisfies a specified HRDI threshold. In some examples, the HRDI may be compared to a specified HRDI threshold and the heart rate mode may be compared to a heart rate mode threshold. An indication of AF may be generated when the determined heart rate mode satisfies a heart rate mode threshold or the determined HRDI satisfies an HRDI threshold. "or" is intended to be non-exclusive. Thus, in the examples of fig. 8 and 9, an indication of AF may be generated for the patient when the heart rate pattern of the patient's heart rate sample is greater than 100bpm, when the HRDI of the sample is less than 25%, or when the heart rate pattern of the heart rate sample is greater than 100bom and the HRDI is less than 25%.

Fig. 10 shows a block diagram of portions of an example of an ambulatory medical device. The apparatus 1005 includes a sensing circuit 1007 and an arrhythmia detection circuit 1010. The sensing circuit 1007 generates a sensed physiological signal representative of cardiac activity of the subject. In certain examples, the sensing circuit 1007 will be electrically coupled to an implantable electrode included in a lead arranged for placement of an implantable object in a ventricle. In certain examples, the sensing circuit 1007 will be electrically coupled to an implantable electrode included in a leadless implantable medical device. In certain examples, the sensing circuitry 1007 will be electrically coupled to an implantable electrode configured to sense cardiac signals without being in contact with the subject's direct heart (e.g., a subcutaneous implantable electrode). In certain examples, the sensing circuit 1007 and arrhythmia detection circuit 1010 are included in a wearable device or a handheld device.

In some examples, the sensing circuit 1007 is a heart sound sensing circuit (e.g., an accelerometer). Heart sounds are associated with mechanical vibrations from the activity of the patient's heart and the flow of blood through the heart. Each heart cycle reproduces heart sounds and is separated and classified according to the activity associated with the vibrations. The first heart sound (S1) is a vibrational sound produced by the heart during mitral valve tightening. The second heart sound (S2) marks the beginning of diastole. The third heart sound (S3) and the fourth heart sound (S4) are related to the filling pressure of the left ventricle during diastole. The heart sound signal may be an electrical signal representing one or more heart sounds produced by the heart sound sensor circuit. The heart sound signals may be used to determine heart rate and depolarization interval.

The arrhythmia detection circuit 1010 may include a microprocessor, digital signal processor, Application Specific Integrated Circuit (ASIC), or other type of processor that interprets and executes instructions included in software or firmware. The arrhythmia detection circuit 1010 can use the sensed physiological signals to determine a ventricular depolarization (V-V) interval and monitor the interval. The arrhythmia detection circuit 1010 may include a peak detector circuit for detecting R-waves in the sensed physiological signal to determine the V-V interval. Arrhythmia detection circuit 1010 may sample the V-V interval and store the samples in memory.

The arrhythmia detection circuit 1010 may determine the distribution of V-V intervals, such as by using a memory to bin intervals and determine the number of intervals per bin. From the V-V interval distribution, the arrhythmia detection circuit 1010 determines HRDI. In some examples, the arrhythmia detection circuit 1010 determines the HRDI as a portion of samples of the V-V interval distribution corresponding to the most frequently occurring V-V intervals in the distribution. The arrhythmia detection circuit 1010 uses the HRDI to generate an indication of AF. In some examples, the arrhythmia detection circuit 1010 compares the HRDI to a specified HRDI threshold and generates an indication of AF when the determined HRDI satisfies the threshold.

In some examples, arrhythmia detection circuit 1010 uses the V-V interval to determine a heart rate pattern. Arrhythmia detection circuit 1010 uses heart rate mode and HRDI to generate an indication of AF. In some examples, arrhythmia detection circuitry 1010 generates an indication of AF when the determined heart rate mode satisfies a specified heart rate mode threshold or the determined HRDI satisfies a specified HRDI threshold. The heart rate mode and HRDI may be determined for a specified duration. In certain variations, the heart rate mode and HRDI may be determined for physiological signals sensed and stored in a memory of device 1000.

According to some examples, the determination of AF using heart rate mode and HRDI may be combined with other methods of determining AF. For example, in some examples, the arrhythmia detection circuit 1010 may combine the determination of AF using ventricular interval dispersion with the determination of AF using heart rate mode and HRDI.

Fig. 11 shows a representation of a sensed physiological signal 1105. The signal is shown with a plurality of R-waves 1110. The V-V interval may be determined as an interval between R-waves. RR1 in the figure refers to the first interval between the first two R-waves; RR2 is the second interval between the second R-wave and the third R-wave, and so on. The difference between the V-V intervals is referred to as Δ RR_1,2(e.g., difference between RR2 and RR 1), Δ RR_2,3And so on.

Fig. 12 shows an example of a sensed physiological signal having a first region 1205 corresponding to NSR and a second region 1210 corresponding to AF. In the NSR region, the V-V spacing will be more regular and the difference in V-V spacing will be small. In the AF area, the V-V intervals will be more dispersed, and the V-V interval difference will be more variable than the NSR.

Fig. 13 is a flow chart of another example of a method 1300 of operating an ambulatory medical device.

Blocks

1305, 1310 and 1315 are performed to determine the heart rate mode and HRDI as described with respect to

blocks

505, 510 and 515 of fig. 5. The arrhythmia detection circuit 1010 of fig. 10 determines differences between the monitored V-V intervals at 1307, and uses the determined V-V interval differences to determine a measure of V-V interval dispersion at 1313. In some examples, the measure of the V-V interval dispersion includes a determined variance of the determined interval difference. To detect AF, the arrhythmia detection circuit 1010 uses a measurement of ventricular interval dispersion, the determined heart rate pattern, and the determined HRDI.

At 1317, the arrhythmia detection circuit 1010 compares the determined heart rate mode to a specified heart rate mode threshold and compares the determined HRDI to a specified HRDI threshold. At 1319, the arrhythmia detection circuit 1010 compares the measure of V-V interval dispersion to a specified dispersion threshold (e.g., compares the measure of V-V interval variance to a specified variance threshold). At 1320, the arrhythmia detection circuit 1010 determines: i) whether the determined measure of V-V dispersion meets a specified dispersion threshold, and ii) whether the determined heart rate pattern meets a specified heart rate pattern threshold or whether the determined HRDI meets a specified HRDI threshold. If so, at 1325, the arrhythmia detection circuit 1010 generates an indication of AF. In other words, the arrhythmia detection circuit 1010 generates an indication of AF when the criteria for the two methods of detecting AF are satisfied.

In some examples, the arrhythmia detection circuit 1010 determines a measure of V-V interval dispersion over a different duration than that used to determine the heart rate mode and HRDI. In an illustrative example intended to be non-limiting, the arrhythmia detection circuit 101 may determine a measure of ventricular interval dispersion over a window of a specified number of cardiac cycles (e.g., 100-.

Other measures of ventricular interval dispersion may be used in combination with the methods of heart rate mode and HRDI to detect AF. In some examples, arrhythmia detection circuit 1010 determines differences in V-V intervals and classifies the interval differences as one of stable, unstable, or unstable and random. In some variations, the intervals are classified as stable bins, unstable bins, or unstable random bins.

An interval difference may be classified as stable when the interval difference is less than a specified threshold difference value from an immediately preceding interval difference. The interval difference may be classified as unstable when the interval difference is greater than the immediately preceding interval difference by a specified threshold difference value, and as unstable-random when the magnitude of the interval difference is greater than the immediately preceding interval difference by the specified threshold difference value and the interval difference is a negative value, which satisfies a specified negative value threshold.

In some examples, the threshold difference value is a value corresponding to a rate difference between two intervals of less than 10 bpm. Thus, if RR2 in FIG. 11 is 1000ms corresponding to 60bpm and RR1 is 857ms corresponding to 70bpm, the interval difference Δ RR_1,2Are binned as stable. If RR1 is less than 857ms, the interval difference is binned as unstable. If RR2 is less than 857ms, and RR1 equals 1000ms, the interval difference Δ RR_1,2Binned as unstable random. In some examples, if the intervals used (e.g., intervals RR1 and RR2) are included in a triplet of three ventricular beats that is longer than the specified minimum interval (e.g., an interval of 324ms corresponding to a heart rate of 185 bpm), the interval differences are only considered for binning.

Returning to the example of fig. 12, in the NSR region, more of the V-V interval difference will be stable. In the AF area, the number of unstable V-V interval differences and unstable random V-V interval differences will increase relative to the number of stable V-V interval differences. The arrhythmia detection circuit 1010 may determine a first metric of ventricular interval difference distribution using the number of stable interval differences and the number of unstable interval differences. The first metric may include a first ratio determined using the number of settling interval differences and the number of unstable interval differences (e.g., the first ratio ═ unstable/stable).

The arrhythmia detection circuit 1010 may use the determined portion of the unstable random interval differences to determine a second metric of ventricular interval difference distribution. The second metric may include a second ratio determined using the number of unstable random interval differences and including a sum of the number of stable interval differences and the number of unstable interval differences (e.g., the second ratio ═ unstable random)/(stable + unstable)).

In the case where the first and second metrics are ratios, since the number of unstable interval differences will increase, the value of the first ratio will increase when AF is present. The value of the second ratio will tend to increase in the presence of AF, since the number of unstable random interval differences will increase. Arrhythmia detection circuit 1010 compares the determined first ratio to a specified first ratio threshold (e.g., a ratio of 3) and compares the determined second ratio to a specified second ratio threshold (e.g., a ratio of 0.06 or 6%). Arrhythmia detection circuit 1010 generates an indication of AF when i) the first ratio satisfies a specified first ratio threshold and the determined second ratio satisfies a specified second ratio threshold, and ii) the determined heart rate pattern satisfies a specified heart rate pattern threshold or the determined HRDI satisfies a specified HRDI threshold, both.

If the apparatus 1005 is a diagnostic only apparatus (e.g., an ILR), the generated indication of AF may be stored as an event in memory and may be stored in association with a timestamp when AF was detected. If the device 1005 is therapeutic, the device 1005 may include therapy circuitry 1015 that may be coupled to the electrodes to provide anti-arrhythmic cardiac therapy, such as anti-arrhythmic pacing energy or high energy shock therapy, such as cardioversion therapy or defibrillation therapy, to the subject. The apparatus 1005 may include a control circuit 1020 to initiate delivery of the anti-arrhythmic therapy in response to the generated indication of AF.

Different methods of combined detection of AF may have different advantages and disadvantages. By tuning the detection of the individual detection methods separately, the different methods can be combined into a fuzzy detection method.

For example, in the example of ratios described above, one or any combination of the specified first ratio threshold, the specified second ratio threshold, the specified heart rate mode threshold, and the specified HRDI threshold may be adjustable in arrhythmia detection circuit 1010. In this way, one criterion to detect AF may be more sensitive than the other criterion.

For example, one or both of the specified first ratio threshold and the specified second ratio threshold may be tuned to be more sensitive to detection of AF than the specified heart rate mode threshold and the specified HRDI threshold. In an illustrative example intended to be non-limiting, the threshold for the unstable/stable ratio may be lowered (e.g., from 3.0 to 2.7) to be more easily met by the detected cardiac event. The unstable random ratio threshold may be maintained at a normal threshold of 6%, the HRDI threshold may be maintained at 0.3, and the heart rate mode threshold may be maintained at 100 bpm.

Alternatively, one or both of the specified heart rate mode threshold and the specified HRDI threshold may be tuned to be more sensitive to detection of AF than the specified first ratio threshold and the specified second ratio threshold. As another illustrative example, which is intended to be non-limiting, the threshold of HRDI may be increased from 0.25 to 0.30 to be more easily met by detected cardiac events. The heart rate mode threshold may be maintained at 100bpm, the unstable/stable ratio threshold may be maintained at 3, and the unstable random ratio threshold may be maintained at 6%.

Fig. 14 shows a block diagram of portions of an example of a medical device system 1400. The system includes an ambulatory medical device 1405. The ambulatory medical device 1405 includes: a sensing circuit 1407 that generates a sensed physiological signal representative of cardiac activity of the subject; and a control circuit 1420. Control circuit 1420 may include a microprocessor, digital signal processor, Application Specific Integrated Circuit (ASIC), or other type of processor that interprets and executes instructions included in software or firmware. The control circuitry 1420 may include other circuitry to perform the described functions. These circuits may include software, hardware, firmware, or any combination thereof. Multiple functions may be performed in one or more circuits as desired.

The control circuit 1420 includes an arrhythmia detection circuit 1410 or sub-circuit that monitors the V-V interval using the physiological signals sensed by the sensing circuit 1407. Arrhythmia detection circuit 1410 uses the V-V interval to determine a heart rate mode and HRDI. Arrhythmia detection circuit 1410 determines a difference between the monitored V-V intervals and uses the determined V-V interval difference to determine a measure of V-V interval dispersion.

Arrhythmia detection circuit 1410 compares the determined heart rate mode to a specified heart rate mode threshold, compares the determined HRDI to a specified HRDI threshold, and compares a measure of the determined V-V interval dispersion to a specified dispersion threshold. Arrhythmia detection circuit 1410 generates an indication of AF when i) the determined measure of V-V interval dispersion satisfies a specified dispersion threshold, and ii) the determined heart rate mode satisfies a specified heart rate mode threshold or the determined HRDI satisfies a specified HRDI threshold, both.

In some examples, the ambulatory medical device 1405 is a wearable medical device or a handheld medical device and includes a user interface 1425 that receives one or more of a specified dispersion threshold, a specified heart rate mode threshold, and a specified HRDI threshold. The user interface 1425 may include one or more of a display, a mouse, a keyboard, and a touch-sensitive or multi-touch-sensitive display screen. The threshold values received through the user interface may be used to tune the AF detection by the ambulatory medical device 1405.

In some examples, the ambulatory medical device 1405 includes a communication circuit 1430 that wirelessly communicates information with a separate device. The system 1400 may include a second device 1435. The second device 1435 includes a user interface 1440 to receive values for one or more of a specified dispersion threshold, a specified heart rate mode threshold, and a specified HRDI threshold. The second device 1435 also includes a communication circuit 1445, and the communication circuit 1445 wirelessly transmits one or more values to the ambulatory medical device 1405. The second device 1435 allows the user to tune thresholds for implantable and wearable or handheld medical devices.

The user interface 1440 may present information to assist the user in setting thresholds for one or both of heart rate mode and HRDI. In certain variations, the user interface 1440 presents suggested values for heart rate mode and HRDI threshold. In certain variations, the user interface 1440 presents graphs, such as the graphs shown in fig. 6 and 7, to the user to present distributions useful for the user to select a heart rate mode or a threshold of HRDI.

In some examples, the threshold of the detection method is automatically tuned by the system 1400. The second means 1435 can include a processor circuit 1450. Processor circuit 1450 may include a microprocessor, Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), or other type of processor that interprets and executes instructions included in software or firmware. The second device 1435 can also include a memory circuit 1455 integral to the processor circuit 1450 or in electrical communication with the processor circuit 1450.

The memory circuit 1455 may store information associated with one or more recorded arrhythmia episodes. The episode may be sensed by the ambulatory medical device 1401 and transmitted to the second device 1435. The processor circuit 1450 uses the stored information to determine AF and adjusts the value of one or more of the specified dispersion threshold, the specified heart rate mode threshold, and the specified HRDI threshold in accordance with the determination of AF. In some examples, an arrhythmia episode is presented via a user interface and a user inputs an assessment or determination of whether the episode represents AF. The processor circuit 1450 then adjusts the value of one or more of the specified dispersion threshold, the specified heart rate mode threshold, and the specified HRDI threshold according to the indication of AF received via the user interface.

In certain embodiments, processor circuit 1450 executes a learning algorithm to determine an adjustment to the threshold. This may include determining performance measures for AF detection by the ambulatory medical device 1401. Performance measures may include sensitivity, specificity, positive predictive value, or negative predictive value, among others. Sensitivity refers to the ability of the detection scheme of the device to effectively detect AF or distinguish AF from noise. Specificity refers to the ability of the detection protocol to mistake for AF a rhythm that is not AF. If the performance measurements do not meet specified performance criteria, processor circuit 1450 may adjust or tune one or more thresholds. Thus, the processor circuit may tune the respective detection methods separately.

Indeed, optimizing an AF detection scheme may involve solving tradeoffs between performance measures, such as, for example, tradeoffs between sensitivity and specificity. The ability to tune one detection method for sensitivity (e.g., to more easily meet a threshold) and a second detection method for specificity (e.g., to more easily meet a threshold) separately can improve the overall performance of the combined AF detection method.

Additional notes and examples

Example 1 may include a subject matter (such as an apparatus) comprising: a sensing circuit configured to generate a sensed physiological signal representative of cardiac activity of a subject; and an arrhythmia detection circuit. The arrhythmia detection circuit is configured to monitor information corresponding to a ventricular depolarization (V-V) interval using the sensed physiological signal; determining a V-V interval distribution of the V-V interval samples; determining a Heart Rate Density Index (HRDI) as a portion of a sample of the V-V interval distribution corresponding to the V-V interval that most frequently occurs in the distribution; and generate an indication of Atrial Fibrillation (AF) using the HRDI.

In example 2, the subject matter of example 1 optionally includes arrhythmia detection circuitry configured to: determining a heart rate pattern as a heart rate corresponding to the V-V interval value having the most samples in the V-V interval distribution; determining the HRDI as part of the V-V interval having the heart rate mode; and generate an indication of AF using the heart rate mode and the HRDI.

In example 3, the subject matter of one or both of examples 1 and 2 optionally includes arrhythmia detection circuitry configured to: comparing the heart rate pattern to a specified heart rate pattern threshold; comparing the HRDI to a specified HRDI threshold; and generating an indication of AF when the determined heart rate mode satisfies a specified heart rate mode threshold or the determined HRDI satisfies an HRDI threshold.

In example 4, the subject matter of one or any combination of examples 1-3 optionally includes arrhythmia detection circuitry configured to: determining a difference between the monitored V-V intervals; determining a measure of the V-V interval dispersion using the determined V-V interval difference; comparing the measured value of the V-V interval dispersion with a specified dispersion threshold value; and generating an indication of AF when i) the measure of the determined V-V dispersion meets a specified dispersion threshold, and ii) the determined heart rate pattern meets both a specified heart rate pattern threshold or the determined HRDI meets a specified HRDI threshold.

In example 5, the subject matter of example 4 optionally includes a measure of V-V interval dispersion including a variance of the determined interval difference; and wherein the arrhythmia detection circuit is configured to: an indication of AF is generated when i) the determined variance satisfies a specified variance threshold, and ii) the determined heart rate mode satisfies both a specified heart rate mode threshold or the determined HRDI satisfies a specified HRDI threshold.

In example 6, the subject matter of one or both of examples 4 or 5 optionally includes a measurement of V-V interval dispersion, comprising: a first ratio determined using the number of stable interval differences and the number of unstable interval differences; and a second ratio determined using the number of unstable random interval differences and a sum comprising the number of stable interval differences and the number of unstable interval differences; and wherein the arrhythmia detection circuit is configured to: an indication of AF is generated when i) the first ratio satisfies a specified first ratio threshold and the determined second ratio satisfies a specified second ratio threshold, and ii) the determined heart rate pattern satisfies both a specified heart rate pattern threshold or the determined HRDI satisfies a specified HRDI threshold.

In example 7, the subject matter of example 6 optionally includes arrhythmia detection circuitry configured to classify the interval difference as stable when the interval difference is less than an immediately preceding interval difference by a specified threshold difference value; classifying the interval difference as unstable when the interval difference is greater than an immediately preceding interval difference by a specified threshold difference value; and classifying the interval difference as unstable random when the amplitude of the interval difference is greater than the immediately preceding interval difference by a specified threshold difference value and the interval difference is a negative value satisfying a specified negative value threshold.

In example 8, the subject matter of one or both of examples 5 and 6 optionally includes: one or more of the specified first ratio threshold, the specified second ratio threshold, the specified heart rate mode threshold, and the specified HRDI threshold are adjustable to cause the specified first ratio threshold and the specified second ratio threshold to be more sensitive to detection of AF than the specified heart rate mode threshold and the specified HRDI threshold, or to cause the specified heart rate mode threshold and the specified HRDI threshold to be more sensitive to detection of AF than the specified first ratio threshold and the specified second ratio threshold.

In example 9, the subject matter of one or any combination of examples 4-8 optionally includes arrhythmia detection circuitry configured to determine a measure of V-V interval dispersion for a different duration than is used to determine the heart rate mode and the HRDI.

In example 10, the subject matter of one or any combination of examples 1-9 optionally includes: a therapy circuit configured to be coupled to the electrode to provide anti-arrhythmic cardiac therapy to the subject; and a control circuit configured to initiate delivery of the anti-arrhythmic therapy in response to the generated indication.

In example 11, the subject matter of one or any combination of examples 1-10 optionally includes sensing circuitry configured to be coupled to an implantable electrode included in a lead arranged for placement of the implantable object in the ventricle.

In example 12, the subject matter of one or any combination of examples 1-11 optionally includes sensing circuitry configured to be coupled to an implantable electrode included in the leadless implantable medical device.

In example 13, the subject matter of one or any combination of examples 1-12 optionally includes sensing circuitry configured to be coupled to a subcutaneous implantable electrode configured to sense cardiac signals without direct cardiac contact with the subject.

In example 14, the subject matter of one or any combination of examples 1-13 optionally includes sensing circuitry and arrhythmia detection circuitry included in the wearable device or the handheld device.

Example 15 may include subject matter (such as a method of operating an ambulatory medical device, a device for performing an action, or a machine-readable medium comprising instructions that, when executed by a machine, cause the machine to perform an action), or may optionally be combined with the subject matter of one or any combination of examples 1-14 to include such subject matter, including: monitoring information corresponding to a ventricular depolarization (V-V) interval of a subject; determining a V-V interval distribution using the sampled V-V interval values; determining a Heart Rate Density Index (HRDI) as a portion of the sampled V-V interval values corresponding to the V-V intervals that occur most frequently in the distribution; comparing the HRDI to a specified HRDI threshold; and is

An indication of AF is generated when the determined HRDI satisfies the HRDI threshold.

In example 16, the subject matter of example 15 can optionally include determining the heart rate mode as the heart rate corresponding to the V-V interval value having the most samples in the V-V interval distribution; determining the HRDI as part of the V-V interval having the heart rate mode; comparing the heart rate pattern to a specified heart rate pattern threshold; and generating an indication of AF when the determined heart rate mode satisfies a specified heart rate mode threshold or the determined HRDI satisfies an HRDI threshold.

Example 17 may include a subject matter (such as a system including an ambulatory medical device), or may optionally be combined with the subject matter of one or any combination of examples 1-16 to include a subject matter comprising: an ambulatory medical device including a sensing circuit configured to generate a sensed physiological signal representative of cardiac activity of a subject; and a control circuit. The control circuit optionally includes an arrhythmia detection circuit configured to: monitoring a ventricular depolarization (V-V) interval using the sensed physiological signal; determining a heart rate pattern using the V-V interval; determining a Heart Rate Density Index (HRDI) using the V-V interval, wherein the HRDI is a portion of the V-V interval having a heart rate mode; determining a difference between the monitored V-V intervals; determining a measure of the V-V interval dispersion using the determined V-V interval difference; comparing the determined heart rate mode to a specified heart rate mode threshold and comparing the determined HRDI to a specified HRDI threshold; comparing the determined V-V interval dispersion measurement value with a specified dispersion threshold value; and generating an indication of AF when i) the measure of the determined V-V interval dispersion meets a specified dispersion threshold, and ii) the determined heart rate pattern meets both a specified heart rate pattern threshold or the determined HRDI meets a specified HRDI threshold.

In example 18, the subject matter of example 17 optionally includes a second apparatus and an ambulatory medical apparatus including communication circuitry configured to communicate information with the second apparatus. The second device includes: a communication circuit configured to communicate with an ambulatory medical device; a memory circuit configured to store information associated with recorded arrhythmia episodes; and a processor circuit configured to determine AF using the stored information and to adjust the value of one or more of the specified dispersion threshold, the specified heart rate mode threshold, and the specified HRDI threshold in accordance with the determination of AF.

In example 19, the subject matter of example 17 optionally includes a second apparatus and an ambulatory medical apparatus including communication circuitry configured to communicate information with the second apparatus. The second device comprises a user interface configured to receive values for one or more of a specified dispersion threshold, a specified heart rate mode threshold, and a specified HRDI threshold; and a communication circuit configured to communicate the one or more values to the ambulatory medical device.

In example 20, the subject matter of claim 17 optionally includes an ambulatory medical device comprising a user interface configured to receive one or more of a specified dispersion threshold, a specified heart rate mode threshold, and a specified HRDI threshold.

Example 21 can include, or can optionally be combined with, any portion or combination of any portions of any one or more of examples 1-20 to include a subject matter, which can include: an apparatus for performing any one or more of the functions of examples 1-20, or a machine-readable medium comprising instructions which, when executed by a machine, cause the machine to perform any one or more of the functions of examples 1-20.

These non-limiting examples may be combined in any permutation or combination.

The foregoing detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings illustrate by way of illustration specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as "examples". All publications, patents, and patent documents cited in this document are incorporated by reference in their entirety as if individually incorporated by reference. The use of one or more references incorporated by reference should be considered supplementary to the present document if there is no agreement in the usage between the present document and those incorporated by reference; for irreconcilable inconsistencies, the usage in this document controls.

In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, regardless of any other circumstance or usage of "at least one" or "one or more". In this document, the term "or" is used to refer to a non-exclusive or, such that "a or B" includes "a but not B," "B but not a," and "a and B," unless otherwise indicated. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein". Furthermore, in the following claims, the terms "comprises" and "comprising" are open-ended, that is, a system, apparatus, article, or process that comprises elements in addition to those listed after such term is still considered to be within the scope of that claim. Furthermore, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

The method examples described herein may be at least partially machine-implemented or computer-implemented. Some examples may include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform a method as described in the examples above. Implementations of such methods may include code, such as microcode, assembly language code, or a high-level language code, to name a few. Such code may include computer readable instructions for performing various methods. The code may form part of a computer program product. Further, during execution or at other times, the code may be tangibly stored on one or more volatile or non-volatile computer-readable media. These computer-readable media may include, but are not limited to, hard disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, Random Access Memories (RAMs) and Read Only Memories (ROMs), and the like. In some examples, the carrier medium may carry code to implement the method. The term "carrier medium" may be used to refer to the carrier wave on which the code is transmitted.

The above description is intended to be illustrative and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments may be used, such as by one of ordinary skill in the art, upon reading the above description. The abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure, in accordance with 37c.f.r. § 1.72 (b). It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Furthermore, in the foregoing detailed description, various features may be grouped together to simplify the present disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. An atrial fibrillation detection device comprising:

a sensing circuit configured to generate a sensed physiological signal representative of cardiac activity of a subject; and

an arrhythmia detection circuit configured to:

monitoring information corresponding to ventricular depolarization V-V intervals using the sensed physiological signal;

determining a V-V interval distribution;

determining a Heart Rate Density Index (HRDI) as a portion of a sample of a V-V interval distribution corresponding to a V-V interval that occurs most frequently in the distribution; and is

Generating an indication of atrial fibrillation, AF, using the HRDI.

2. The apparatus of claim 1, wherein the arrhythmia detection circuit is configured to:

determining a heart rate mode as a heart rate corresponding to the V-V interval value having the most samples in the V-V interval distribution;

determining the HRDI as part of a V-V interval having the heart rate mode; and is

Generating an indication of AF using the heart rate mode and the HRDI.

3. The apparatus of claim 2, wherein the arrhythmia detection circuit is configured to compare the heart rate mode to a specified heart rate mode threshold; and generating an indication of the AF when the determined heart rate mode satisfies the specified heart rate mode threshold or the determined HRDI satisfies an HRDI threshold.

4. The apparatus of claim 2 or 3, wherein the arrhythmia detection circuit is configured to:

determining a difference between the monitored V-V intervals;

determining a measure of the V-V interval dispersion using the determined V-V interval difference;

comparing the measure of V-V interval dispersion to a specified dispersion threshold; and is

Generating the indication of AF when i) the measure of the determined V-V dispersion satisfies the specified dispersion threshold, and ii) the determined heart rate pattern satisfies the specified heart rate pattern threshold or the determined HRDI satisfies a specified HRDI threshold, both i) and ii) being satisfied.

5. The apparatus of claim 4, wherein the measure of V-V interval dispersion comprises a variance of the determined interval differences; and wherein the arrhythmia detection circuit is configured to: generating an indication of the AF when i) the determined variance satisfies a specified variance threshold, and ii) the determined heart rate mode satisfies the specified heart rate mode threshold or the determined HRDI satisfies the specified HRDI threshold, both i) and ii) being satisfied.

6. The apparatus of claim 4, wherein the first and second electrodes are disposed on opposite sides of the substrate,

wherein the measurement of the V-V interval dispersion includes: a first ratio and a second ratio, wherein the first ratio is determined using a number of stable interval differences and a number of unstable interval differences; and the second ratio is determined using the number of unstable random interval differences and a sum comprising the number of stable interval differences and the number of unstable interval differences; and is

Wherein the arrhythmia detection circuit is configured to: generating an indication of the AF when i) the first ratio satisfies a specified first ratio threshold and the determined second ratio satisfies a specified second ratio threshold, and ii) the determined heart rate mode satisfies the specified heart rate mode threshold or the determined HRDI satisfies the specified HRDI threshold, both i) and ii).

7. The apparatus of claim 6, wherein the arrhythmia detection circuit is configured to: classifying an interval difference as stable when the interval difference is less than a specified threshold difference value from an immediately preceding interval difference; classifying the interval difference as unstable when the interval difference is greater than the specified threshold difference value than an immediately preceding interval difference; and classifying the interval difference as unstable random when the amplitude of the interval difference is greater than the immediately preceding interval difference by the specified threshold difference value and the interval difference is a negative value that satisfies a specified negative value threshold.

8. The apparatus of claim 6, wherein one or more of the specified first ratio threshold, the specified second ratio threshold, the specified heart rate mode threshold, and the specified HRDI threshold are adjustable to cause the specified first ratio threshold and the specified second ratio threshold to be more sensitive to detection of AF than the specified heart rate mode threshold and the specified HRDI threshold, or to cause the specified heart rate mode threshold and the specified HRDI threshold to be more sensitive to detection of AF than the specified first ratio threshold and the specified second ratio threshold.

9. The apparatus of claim 4, wherein the arrhythmia detection circuit is configured to determine a measure of V-V interval dispersion for a different duration than is used to determine the heart rate mode and HRDI.

10. The apparatus of any of claims 1-3, comprising: a therapy circuit configured for coupling to the electrode to provide anti-arrhythmic cardiac therapy to the subject; and a control circuit configured to initiate delivery of the anti-arrhythmic therapy in response to the generated indication.

11. The apparatus of any one of claims 1-3, wherein the sensing circuit is configured to be coupled to an implantable electrode included in a lead arranged for placement of an implantable object in a ventricle.

12. The device of any of claims 1-3, wherein the sensing circuit is configured to be coupled to an implantable electrode included in a leadless implantable medical device.

13. The apparatus of any one of claims 1-3, wherein the sensing circuit is configured to be coupled to a subcutaneous implantable electrode configured to sense cardiac signals without direct cardiac contact with the subject.

14. The device of any one of claims 1-3, wherein the sensing circuit and the arrhythmia detection circuit are included in a wearable device or a handheld device.

15. A computer-readable medium comprising instructions that, when executed by a medical device, cause the medical device to perform actions comprising:

monitoring information corresponding to ventricular depolarization V-V intervals of the subject;

determining a V-V interval distribution;

determining a Heart Rate Density Index (HRDI) as a portion of a sample of a V-V interval distribution corresponding to a V-V interval that occurs most frequently in the distribution;

comparing the HRDI to a specified HRDI threshold; and is

Generating an indication of AF when the determined HRDI satisfies the HRDI threshold.